Starting circuit for electric lamps



March 30, 1954* LEMMERS 2,673,942

STARTING CIRCUIT FOR ELECTRIC LAMPS Filed Oct. 26, 1948 4 Sheets-Sheet 1 i fa Inverwtov: BLQTTS Lemmevs 9 Mm His Abboffig STA/PT l/OLTS March 30, 1954 Filed Oct. 26, 1948 4 Sheets-Sheet 3 Fi s.

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March 30, 1954 ER 2,673,942

STARTING CIRCUIT FOR ELECTRIC LAMPS Filed Oct. 26, 1948 4 Sheets-Sheet 4 'lnveniiorz Eu ene Lemmers, 8 iv 5 I His Art'tovneg,

Patented Mar. 30,1954

2,673,942 STARTING CIRCUIT FOR ELECTRIC LAMPS Eugene Lemmers, Cleve signor' to General Ele ration of New York land Heights, Ohio, asctric Company, a corpo- Application October 26, 1948, Serial No. 56,615

8 Claims.

My invention relates to starting and operating circuits for electric discharge devices, and more particularly to starting and operating circuits for low pressure mercury vapor discharge devices, such as fluorescent lamps, and has resulted from my discovery that, with fluorescent lamps employing krypton or xenon as a starting gas, totally unexpected advantages ensue from the application of an auxiliary potential, diiferent from that applied to either electrode, to a starting stripe external to the lamp. These unexpected advantages occur within a fairly restricted range of voltages, and I claim, in this application, combinations of krypton and/or xenon filled lamps with means for utilizing this restricted range to the best advantage in starting such lamps.

I also disclose in the present application, various novel circuits for applying an auxiliary po tential to a starting stripe or electrode. These circuits have in common the feature of utilizing dissimilar phase voltages, applied to the electrodes of each lamp of a pair as auxiliary starting potentials for the other lamp. In a preferred embodiment, this feature is brought about by means of a novel cross-over connection. These circuits may be used with other types of electric discharge devices besides the krypton or xenon filled lamps with which this parent application is particularly concerned. Accordingly, they are claimed in my divisional application No. 142,457, filed February l, 1950, and assigned to the same assignee as the present invention.

Generally speaking, according to the prior art arrangements for starting and operating low pressure electric discharge devices, such as fluorescent lamps, employing mercury vapor at a relatively low pressure ranging from several microns of mercury to 10 to 30 microns of mer cury, and employing a starting gas, it has been conventional to use the preheating type starting circuit and or to employ the instant starting type circuit. wherein a substantially greater voltage is impressed across the electrodes of the lamp in order to render the lamp conducting immediately upon energization of the circuit.

In co-pending patent application Serial No. 731,428, filed February 28, 1947, now U. S. Patent 2,504,549, Lemmers et al., there is disclosed and claimed a starting and operating circuit for electric discharge devices, such as low pressure mercury vapor fluorescent lamps, wherein preheating and instant starting operation are ac" complished, obtaining the results and benefits of both the instant-start and preheating methods Without incurring any material disadvantage. The above-identified application is assigned to the assignee of this application. 7

Where krypton and xenon, or mixtures thereof, are employed as the filling or starting gas in a low pressure mercury vapor discharge device, it has been found that in many instances the previously available starting circuits are not adequate to provide the requirements of theimproved type of fluorescent lamp, it being indicated that larger starting voltages would be required as well as ballasts which operate at lower voltages after the arc discharges are established. At any rate, it has become necessary to provide new and improved starting circuits for lamps employing krypton, xenon, or mixtures thereof and which do not involve voltages so high as to make general and widespread use undesirable.

The general object of my invention is to provide new and improved starting circuits for low pressure electric discharge devices.

A more specific object of my invention is to provide new and improved electric circuits for starting and operating low pressure fluorescent lamps employing krypton, xenon, or mixtures thereof, as the starting gas in addition to the usual mercury vapor.

Briefly stated, in accordance with the illustrated embodiments of my invention I provide new and improved starting circuits for low pressure mercury vapor fluorescent lamps which employ krypton, or xenon, or mixtures thereof either alone or with argon, and which also inelude an associated starting means which may take the form of a conductive stripe adherent to the surface of the elongated envelope of the lamp. Preferably, this starting stripe may be positioned on the outside surface of the lamp envelope. It has been-surprising tonote in connection with the work which I have conducted that while throughout a certain range the voltage required to initiate an arc discharge between electrodes of such a lamp decreases as the voltage impressed on the starting stripe is increased, there is a point reached beyond which it is inadvisable to further increase the starting stripe voltage. There are several reasons for this conclusion. From a strictly engineering point of view, there is a point attained beyond which it is inadvisable to go because a further increase in starting stripe voltage does not reduce the lamp starting voltage. For-example, I have found that irrespective of the lamp length it is inadvisable to increase the stripe voltage to'a value greater than 300 volts, and it is entirely satisfactory to maintain the starting stripe voltage within a range from about 150 to 300 volts. Once this optimum range has been obtained, very little if any additional lowering of lamp starting voltage is achieved by going beyond it, thus indicating the second reason for so limiting the starting stripe voltage. This second advantage relates to circuit economy, it being clear that there is no iustification for additional expenditure in apparatus cost to provide equipment to supply higher voltages than required. Lastly, there is a decided advantage from the standpoint of eliminating personnel shock hazard incident to the presence of very high, or unnecessarily high, starting stripe voltages. This factor would be of extreme consequence if the stripe voltage were to be proportionately increased in value as a function of lamp length, as would occur if the voltage were merely increased upon increase of the lamp length.

It has been my observation that at about 150 volts applied to the starting stripe,'irrespective of the lamp length, there is very little or no advantage obtainable in reduction of lamp starting volts, by further increase of the stripe voltage. As an example it is significant to note that this approximate value obtains for lamps 4 feet long and 8 feet long, and which employ krypton at pressures ranging from about 2 mm. to about 3.5 mm. of mercury.

In accordance with a still further feature of my invention I provide an improved circuit for energizing a pair of low pressure mercury vapor fluorescent lamps through interconnected leading power factor and lagging power factor circuits and in which cross-over connections, or other means, are provided for impressing on a starting stripe or starting means associated with one of the electric lamps a voltage derived from the energizing circuit connected to the other lamp. I have found that it is desirable to impress on such starting means a potential not less than about 150 volts with reference to either of the electrodes of a given lamp. Alternatively,

additional winding means may be associated with or constitute a part of a transforming means such as an autotransformer, or separate transforming means may be employed, to obtain the desired difference in potential impressed on the starting stripe with reference to that'of either of the electrodes of a particular lamp.

For a better understanding of my invention reference may be had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to a circuit for energizing a pair of low pressure mercury vapor fluorescent lamps; and Figs. 2 and 3 represent operating characteristics of the preheating-instant start type circuit disclosed and claimed in my co-pending joint patent application Serial No. 731,488. Figs. 4 and 5 represent the relationship between the voltage impressed on the starting stripe and the lamp starting voltage for fluorescent lamps employing krypton as the starting gas. Figs. 6 and '7 illustrate diagrammatically further arrangements in which the desired starting stripe voltage may be supplied to the lamps; and Figs. 8 and 9 are further modifications in which separate winding means, or separate transforming means, respectively. are applied to leading power factor and lagging power factor circuits for energizing a pair of fluorescent lamps. Fig. 10 is astill further modification of my invention wherein the starting stripes of a pair of fluorescent lamps are connected to a single winding means of an autotransformer adapted to supply starting and. operating voltages as well as stripe voltages.

Referring now to Fig. 1 of the accompanying drawings, my invention is there illustrated as applied to a system for starting and operating a pair of low pressure electric discharge devices, such as a pair of low pressure mercury vapor lamps I, l of the fluorescent type. The lamps I, l comprise elongated tubular or cylindrical envelopes 2, 2 having sealed into the ends thereof filamentary electrodes 3, 4 and 5, 6 respectively. Although my invention is not limited in its broader aspects to discharge devices employing filamentary or thermionic electrodes, for the purpose of illustrating my invention in connection with one type of preheating circuit I have chosen to refer to that being disclosed and claimed in the-joint co-pending patent application Serial No. 731,488 and accordingly, the electrodes have been illustrated as of the filamentary or thermionic type. However, in view of the disclosure of the present application, it will be appreciated that electrodes of the cold type (activated or otherwise) may also be employed. Where the electrodes are of the filamentary type it is preferable to employ the coiled-coil type of construction wherein tungsten wire is activated, preferably with oxides of alkaline earth metals such as a mixture of barium and strontium oxides. The envelopes 2, 2 contain gaseous atmospheres, such as starting or filling gases comprising krypton or Xenon, or mixtures thereof, at a pressure ranging from about 2 mm. to about 3.5 mm. of mercury, and also a quantity of mercury which, during operation of the lamps, is at a vapor pressure of the order of several microns to 20 or 30 microns, the preferable operating range under normal ambient temperature conditions being of the order of 10 microns. The fluorescent lamps I, l are provided with a suitable fluorescent material or phosphor coating, preferably on the interior surfaces of the envelopes. This fluorescent coating upon excitation by ultraviolet radiation produced by an electric discharge between co-operating electrodes, transforms the shorter radiation due to the discharge into longer wave radiation such as radiation within the visible range. For ease of starting, I employ starting means I, 'l', of conductive material, and which extends along the axial length of the lamps l, I, and preferably terminates within the vicinities of the electrodes for that lamp. As shown in Fig. 6 described hereinafter, these starting means may comprise conductive or metallic stripes adherent to the elongated envelope, and preferably adherent to the outside surface of the envelope.

The lamps i, l are connected to starting and operating circuits 9, l0 and 10, H. These circuits supply starting and operating voltages to the lamps l, I each starting voltage being substantially higher than the operating voltage. Preferably, these energizing, or starting and operating circuits, have different power factors, that is, one (9, ID) has a lagging power factor and the other (10', II) has a leading power factor. Other terminals of the thermionic electrodes 3, 4 and 5, 6 are connected to terminals labeled: a, b, c, and d, to which may be connected a suitable circuit forsupplying preheating current to the electrodes. The lamps connected to the circuits forming the lagging power factor load circuit 9,10 and the leading power factor load circuit I Il, are-connected across a suitable source of voltage, preferably a voltage step-upauto-transformer I2having a pair of secondary winding means I3 and I4 serving also as ballasts for lamps I, I, respectively, and being loosely coupled to a source of current, such as a primary winding means I5 energized from an alternating current supply circuit I 6. As may be gathered from the drawing, the secondary windings I3 and I 4 are poled to augment the voltage applied across the primary winding I 5, in opposite phases, so that maximum potential difference occurs across the outer ends of the secondary windings I3 and I 4. 'The alternating current supply circuit I6 may bea 115 volt, 60 cycle commercialsource of current. A usual capacitor I1 is connected to the secondary winding means I4 to render circuit III, II, the

leading power factor circuit, by introducing a phase correction or displacement with to the lagging power factor circuit 9, I0.

Where it is desired in the employment of my invention to provide preheating type circuits in respect which the energization of the filamentary or thermionic electrodes is substantially reduced, or reduced to zero, upon initiation of arc discharges within theelectric lamps, I may employ athree voltage neutralizing circuit disclosed and claimed in the above-identified joint application Serial No. 731,488. This circuit is connected to terminals a -d inclusive and may briefly be described as follows.

I may employ tertiary coils or windings I8, I9, 28 and 2| on the core of the auto-transformer I2 and inductively coupled to the transformers primary winding means I5; coils or windings 22, 23, 24 and 25 on the core of the auto-trans former 12 are inductively coupled to the transformer secondary winding means I3; and coils or windings 26, 21,. 28 and 29 on the core of the auto-transformer I2 are inductively coupled to the transformer secondary winding means It. The filamentary electrodes, in this case, are each connected in series with windings inductively coupled to the primary winding means !5 of the auto-transformer l2, and secondary winding means I 3 and I4. Thus, electrodes 3, 4, 5 and 6 are connected in series with inductively coupled auto-transformer windings 22, I 8 and 26; 23, I9

and 21; 24, and 28; and 25, 2I and 29; respectively, and comprises the starting and electrode control or heating circuits 9, 30, I9, 3!, It, 32 and II, 33, respectively. The coils or windings serving electrode 3 and electrode 5, for example, may he wound in the following manner;- the windings 22 and 24 are wound over the secondary winding means I3 of the auto-transformer it in the opposite direction to that of the secondary winding means I3; the winding means I8 and it are wound over the primary winding means it of the auto-transformer I2 in the same direction as the auto-transfo rme1"s primary winding means I 5; and the winding means and 23 for the above electrodes 3 and 5, are wound over the secondary winding means 14 of the autotransformer I2 wound in the reverse direction to the secondary winding means I4. The secondary winding means I3 of the auto-trap former I2 however is wound in the reverse direction to the primary winding section means it and the sec ndar winding'means I4 or the auto-transformer I2. A; suitable manual control switch 34 may be connected in series with'the rimary winding means I5 of transformer I2.

the temperature of the electrodes ciated electrodes of In order to impress on the starting means I, I of the lamps I, i potentials not less than about 150 volts with reference to that of either of the associated electrodes for each lamp, I provide cross-over means or cross-over connections 35 and 36 which are connected to starting means l 7, associated with lamps i and I, respectively. These cross-over connections impress on the starting means for one lamp voltage derived from the starting and energizing circuit connected to the other lamp. It will be further noted that these connections include in series therewith current limiting resistances 8 and 8 which serve to reduce the amount of current which be drawn therefrom in the event of accidental contact. In this manner the personnel shock hazard is further reduced. This current limiting feature in which resistances of predetermined large value are employed is disclosed and being claimed in co-pending patent application Serial No. 733,595, filed March 10, 19?;7, now U. S. Patent 2,512,280, Lemmers.

The above described advantages in respect to the use of krypton, Xenon, or mixtures thereof, concerning the relationship between the starting stripe voltage and the lamp starting voltage applies to the use of the stated gases or combinations of gases either alone or with argon. I have found that where the starting gas compo sition comprises 59 per cent argon, and per cent krypton, xenon, or mixtures thereof, that the characteristics of the latter-mentioned gases are given or imputed to the total starting gas composition, which characteristics are shown in the curves of Figs. 4 and 5. It appears that a small amount of gases from the group consisting of krypton, Xenon, and mixtures thereof, such as from 10 to 15 per cent of the total starting gas composition, will impart to the total starting gas composition the illustrated tapered voltage relationships as shown by the krypton curves in Figs. e and 5.

It should be observed that there is a very definite advantage incident to the use of kryp ton, xenon, or mixtures thereof, either alone or in combination with argon as contrasted with the use of pure argon alone. These advantages are definitely understood by reference to Figs. and 5, it being clear that the reduction starting voltage in the case of argon is very much less than that incident and available in lamps employing krypton, xenon, or mixtures thereof. In other words, there is a very decided advantage in apparatus economy incident to the correlation of starting stripe voltage and lamp starting voltage in lamps employing the lattermentioned group of gases.

When switch 34 is closed, power is supplied to the auto-transformer i2, and its associated and inductively coupled windings are energized. Cathode heating current, suiiicient for raising of each lamp to produce electron emission therefrom and to iacilitate breakdown of the discharge path therebetween is supplied to the lamps. Proper voltage for starting arc discharges between assothe different lamps are also provided and impressed across co-operating electrodes. Simultaneously with the closing of the switch 3d there is impressed on each of the starting means 7 and l a voltage which is suiiiciently high or great with respect to the voltages inipressed on either of the electrodes of the associated lamp to render the lamp conducting without necessitating the use of excessively high starting voltages between electrodes. As stated above, I have found that there is an optimum range of starting stripe voltages lying between the values of about 150 volts and 300- volts which serves this purpose very effectively. A voltage difference on the starting stripe not less than about 150 volts with reference to either of the electrodes has been found to be the value at which the effect of. diminishing utility is encountered concerning the use of voltages for assisting or facilitating the initiation of are discharges. In other words, the electrode or lamp starting voltage isfound to decrease at a disproportionately slow rate for starting stripe voltages in excess of the range from 150 to 300 volts or even in excess of about 150 volts. Stated in yet another way, beyond this range, the increinental decrease or decrement in starting voltage, for further increments in auxiliary starting aid voltage, falls substantially to zero, as may readily be seen !by inspection of Figs. 4 and 5. This has been observed to be true irrespective of the lamp length. For example, by referring to Fig. 4 it will be noted that for a lamp 4 feet long the lamp starting voltage-stripe voltage curve begins to approach a horizontal or uniform value at about 150 or 160 volts in lamps employing krypton at a pressure ranging from about 2 mm. to 3.5 mm. of mercury. This feature is in decided contrast with the characteristic of argon-filled lamps. Likewise, it has been found that a similar condition prevails in a corresponding lamp 8 feet long. This condition and the resuits of tests performed on such lamps are shown in Fig. l

Referring now to the electrode heating circuit shown in Fig. 1, and which is connected to terminals a-d, inclusive, when the switch 34 is closed, preheating current of predetermined magnitude is transmitted to the electrodes 3-6 inclusive. Before an arc discharge occurs in either lamp i or i, induced voltages in each inductively coupled winding of a particular electrode heating circuit, for example circuit Ill, 3|, is either in phase or 180 out of phase with the voltages of the other inductively coupled windings of that heating circuit. Fig. 2 illustrates vectorially the phase relationship and magnitudes of the induced voltages in the windings of heating circuit it, 3 l before an arc discharge is established.

V19 represents the induced voltage of winding l9; V21 represents the induced voltage of winding 2?; and V23 represents the induced voltage of winding 23. Thus, the resultant voltage Va is the voltage which is supplied to the heating circuit i9, 3| and which is impressed across the filamentary electrode 4 and is the voltage used for raising the electrode temperature to facilitate breakdown of the arc discharge path in the lamp and for starting an arc discharge between the electrodes.

After the arc discharge has been established the magnitudes of, and phase relationship among, the induced voltages of the heating circuit H), 31 change. As indicated in Fig. 3, the resultant voltage Va may be substantially reduced to a predetermined operating value by proper proportioning and phasing of the three induced voltages of the control or heating circuit ill, 8!. Perfect neutralization is difficult to obtain because of the voltage drop caused in the lamp filamentary electrode by the phase and magnitude of its arc current. The resultant voltage Via-however, is small enough to be negligible. Perfect correlation between the voltages of the windings to obtain substantial zero operating voltage during lamp conduction is not necessary for the successful operation of the circuit. To summarize, in view of the above it will be appreciated, that upon closing the switch 34 immediately there is applied to each lamp cathode heating current and a predetermined voltage is applied to the associated starting stripe or starting means. As soon as the electron-emission of the electrodes reaches a predetermined value the applied lamp voltage working in conjunction with the potential of the starting means renders the lamp conducting. Thereupon, due to the leakage reactance of the transformer Hi, the starting voltage is reduced to a lower arc-maintaining voltage and the cathode heating circuits through the neutralizing action thereof reduce the cathode or electrode current to substantially zero.

Another modification of my invention is illustrated in Fig. 6 wherein fluorescent lamps 31 and 38, having enclosing envelopes 39 and 40, are provided with electrodes such as filamentary electrodes 4|, 42 and 43, 44, respectively. The lamps 31 and 38 are provided on the associated envelopes with adherent conductive metallic starting stripes 45 and 46. A suitable high leakage reactance auto-transformer 41 having primary winding means 48 and associated secondary winding means 49 and 50 is provided in order to supply starting and operating voltages to .lamps 31 and 38 through circuits 5%, 52 and 53,

54, respectively. A suitable capacitor 55 may be connected in series relation with the primary winding means 48 and the secondary winding means 49 in order to establish phase displacement between the two circuits 5!, 52 and 53, 54 for energizing the lamps. Transformer 4i is energized from a source of alternating current 56. Similar to the arrangement shown in Fig. 1, cross-over connections 51 and 58 for impressing suitable potentials on the starting stripes l5 and 46 of lamps 31 and 38, respectively, are employed to impress thereon potential differences not less than about 150 volts with respect to either of the electrodes of a given lamp. Current limiting resistances 59 and 60 may be connected in the above-stated manner to reduce or completely eliminate personnel shock. hazard.

Electrode or cathode preheat circuits or cathode energizing circuits may be connected to terminals a, b, and c, d, for the lamps in the manner explained above in connection with the circuit of Fig. 1. For example, the same type circuit may be employed if it is desired, although it will be appreciated that my instant invention is not limited to the use of a particular type preheating circuit.

Fig. "I is a further modification of my invention, and is quite similar to the circuit shown in Fig. 6 and corresponding elements have been assigned like reference numerals. In the arrangement shown in Fig. 7 the starting means need not be an integral part of the lamps and may comprise starting means BI and 62 constituted by metallic housings or reflectors of lamp fixtures extending axially the length of the lamps. In addition I may provide separate inductances 53 and 54 which are connected in series relation with conductors 5i and 53, respectively, where additional or separate current controlling means is deemed desirable for lamp operation and ballasting.

I In the modification of the invention shown in Fig. 8 I provide transforming means 65 having primary winding means 66 connected to a suitable source of alternating current 61. The transforming means 65 maybe of the auto-transformer type having a pair of secondary windingmeans B and 69 which supplystartingandoperating voltages to lamps 3 1 and through circuits 10, II and 1|, 12, respectively. In addition'to the secondary winding means I provide tertiary winding means 19-and 14 which'impress onthe starting means GI and lilvoltages different than that existing on either of theassociated electrodes of a lamp by a value not less than about 150 volts. These separate starting stripe voltages are connected through current limiting resistances 59 and 60.

In Fig. 9 there is illustrated diagrammatically a still further modificationof my" invention wherein lamps 15 and 16 having electrodes 11, 18

and 19, 80, and starting means8I- and 02 are energized through an auto-transforming means generally similar in function and arrangement to that shown in the circuit of Fig. 1. transforming means 83 comprises a primary voltage to lamps 15 and 16 through circuits 01,

80 and 80, 89, the latter circuit having in series therewith a capacitor 90 to provide phase displacement to prevent a stroboscopic eiTect of the light emitted by the two lamps. The transforming means 83 is provided with tertiary winding means comprising windings 90-95 inclusive, windings 90, 92 and 94 connected to energize only one of the electrodes of lamp 15, such as electrode 1'1; and windings 9|, 93 and 95 being connected to energize only one electrode of lamp 16 such as electrode 80. A similar set'of windings, of course, may be provided for each of electrodes 10 and 19, if desired. set of three tertiary windings I provide separate transforming means 96and 91'-which serve to impress on the starting means 8I- and 82 voltages sufficiently above that impressed on either of the associated electrodes of a given lamp. For example, transformer 96 has a primary "winding 08 connected in series relation with tertiary windings 90, 92 and 94 and is connected to terminal a,

the secondary winding 99 of this-transformer being connected to the starting means 8| through current-limiting resistance '99. Transformer 91 is connected in a similar manner with respect to lamp 16.

A further modification of my invention is illusstated in Fig. 10 wherein fluorescent lamps I00 and NH having electrodes I02, I03 and I04, I05

are enclosed within elongated envelopes I06 and vicinities cf the electrodes of the associated lamp. These starting means may be metallic stripes ad'- herent to the external surfaces of the envelopes, or may comprise conductive members of a fixture, or other element, extending along the axial di-- mension of the lamp in order to 'provide'the de- In series relation withea'chof the 10 to impress on the starting means I08 and I09 2. voltage'to assist in establishing arc discharges within the lamps. Current limiting resistances H9, and I20 having a common juncture are connected to the starting means I08 and I09, respectively. The voltage provided by the tertiary winding means H0 is of suiiicient value so that the voltage impressed on the starting means I08 and I09 is at least about volts greater than the voltage impressed on either one of the electrodes of a particular lamp. Transforming means II 0 may be energized from a suitable source of alternating current I2I through a starting switch I22. Secondary winding means I I 2 and H3 are loosely coupled with the primary winding means III so that these windings serve as ballasts for the respective connected lamps. Of course, the transforming means II 0 is also designed by virtue of its leakage reactance to provide a lower voltage than the starting voltage after the lamps conduct current. Furthermore, suitable preheating circuits may be connected to the terminals labeled ad in order to preheat the electrodes l02-I05, which operation may be accomplished in the manner explained above in connection with the circuit of Fig. 1.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a supply circuit, an electric discharge device of the low pressure positive thereof at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing upon said starting aid a potential within the lower limits of the region wherein further increase in starting aid potential produces only a negligible decrease in starting voltage, said region beginning at about 150 volts above the voltage of that electrode having the higher potential.

2. In combination, a supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas mixture containing at least 10 per cent of a gas from the group consisting of krypton and xenon and mixtures thereof, said starting gas mixture being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally between the vicinity of said electrodes, said supply circuit comprising means for preheating electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing upon said starting aid a potential within the lower limits of the region wherein further increase in starting aid potential produces only a negligible decrease starting voltage, said region beginning at about 150 volts above the voltage of that electrode having the higher potential.

3. In combination, a supply circuit, an elec tric discharge device ofthe low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas mixture containing at least of a gas from the group consisting of krypton and xenon and mixtures thereof, said starting gas mixture being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing upon said starting aid a potential within the lower limits of the region wherein further increase in starting aid potential produces only a negligible decrease in starting voltage, said region beginning at about 150 volts above the voltage of that electrode having the higher potential.

4. In combination, a supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas mixture containing at least 10% of a gas from the group consisting of krypton and xenon and mixtures thereof, said starting gas mixture being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing on said starting aid a potential slightly in excess of the value whereat the decrement in starting potential falls substantially to zero, said value being in the approximate range of 150 to 300 volts above the voltage of that electrode having the higher potential.

5. In combination, a supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas mixture containing at least 10% of a gas from the group consisting of krypton and xenon and mixtures thereof, said starting gas mixture being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a stripe or narrow ribbon of a conductive coating extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing on said starting aid a potential slightly in excess of the value whereat the decrement in starting potential falls substantially to zero, said value being in the approximate range of 150 to 300 volts above the voltage of that electrode having the higher potential.

6. In combination, an alternating current supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas mixture containing at least 10% of a gas from the group consisting of krypton and xenon and mixtures thereof, said starting gas mixture being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit including transforming means supplying preheating current to said electrodes to raise them to thermionic emission and applying a potential across said electrodes, and separate winding means coupled to said transforming means for impressing on said starting aid a potential slightly in excess of the value whereat the incremental decrease in starting potential falls substantially to zero, said value being in the approximate range of 150 to 300 volts above the voltage of that electrode having the higher potential.

'7. In combination, a supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at opposite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas consisting of up to 50 per cent argon and the remainder one of the group consisting of krypton, xenon and mixtures thereof, said starting gas being at pressures ranging from about 2 to. 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing on said starting aid a potential within the lower limits of the region wherein further increase in starting aid potential produces only a negligible decrease in starting voltage, said region beginning at about 150 volts above the voltage of that electrode having the higher potential.

8. In combination, a supply circuit, an electric discharge device of the low pressure positive column type comprising an elongated envelope and a pair of thermionic electrodes mounted at op-- posite ends therein, an ionizable medium within said envelope comprising mercury and a starting gas consisting of up to per cent argon and the remainder one of the group consisting of krypton, xenon and mixtures thereof, said starting gas being at pressures ranging from about 2 mm. to 3.5 mm., an auxiliary starting aid in the form of a conductor extending longitudinally outside said envelope between the vicinity of said electrodes, said supply circuit comprising means for preheating said electrodes to thermionic emission, means for applying a potential across said electrodes, and means for impressing on said starting aid a potential within the lower limits of the region wherein further increase in starting aid potential produces only a negligible decrease in starting voltage, said region beginning at about volts above the voltage of that electrode having the higher potential.

EUGENE LEMMERS.

References Cited in the file of this patent UNITED STATES PATENTS Number (Other references on following page) Number 13 UNITED STATES PATENTS Name Date Miesse Oct. 23, 1934- Claude Jan. 15, 1935' Beck Aug. 20, 1935 Beck Oct. 22, 1935 De Bruin Oct. 6, 1936 Spanner Jan. 14, 1941 Germer Nov. 11, 1941 Freeman Oct. 13, 1942 Riess et a1. Oct. 27, 1942 Number 14 Name Date Johnson Mar. 9, 1943 Karash Mar. 16, 1943 Ruff Feb. 22, 1949 Found June 21, 1949 Johnson Mar. 7, 1950 Clack et a1 Apr. 18, 1950 OTHER REFERENCES 10 Miller and Fink: Neon Signs, 1st ed., McGraw- Hill, N. Y. C., 1935, pages 42-43. 

